The present invention relates to controllers for opening and closing fluid channels, and more particularly to a controller having the function of indicating that a fluid channel is open or closed.
Controllers are already well known which comprise a valve body having a fluid channel, a casing disposed above the valve body, an operating rod provided within the casing and movable upward and downward, drive means for moving the operating rod upward and downward, and a valve stem movable upward and downward with the upward and downward movement of the operating rod for opening and closing the fluid channel (see, for example, U.S. Pat. No. 5,556,072).
In the case where the fluid for use with such controllers is a noxious gas, it is desired that the controller have the function of indicating that the fluid channel is open or closed when viewed from outside, whereas controllers having such an opening-closing indicating function still remain to be developed for actual use.